The present invention relates generally to metal vapor lasers and more particularly to specifically designed electrode and wicking arrangements associated with such a laser.
One type of metal vapor laser in the prior art is illustrated in FIG. 1A. This laser which is generally indicated by the reference numeral 10 is shown including a plasma tube 12 which forms part of an overall plasma tube assembly. The plasma tube assembly is not only the tube but also a suitable means not shown for thermally insulating the tube which contains a metal vapor, for example copper vapor in a specific embodiment and buffer gas, for example neon. The laser utilizes means including electrode arrangements 14 and 16 located at opposite ends of the plasma tube for electrically heating the interior of the plasma tube in accordance with the profile illustrated in FIG. 1B. Note specifically from this latter figure that the interior of tube 12 increases in temperature from its left-hand end to a maximum constant temperature over an active intermediate volume within the tube and thereafter decreases to a minimum value at the right-hand end of the tube. The temperature within the active volume of the tube is sufficiently high to cause the metal vapor contained within that volume to vaporize and subsequently be electrically excited by the current passing between the electrode arrangements, whereby to initiate the production of the metal vapor laser beam.
It is to be understood that all of the components of metal vapor laser 10 are not illustrated in FIG. 1A and many of these components will not be discussed here. However, in order to appreciate the present invention, the prior art laser illustrated in FIG. 1A is shown including a pair of wicking arrangements generally indicated at 18 and 20. Note that the two wicking arrangements are located within plasma tube 12 near opposite ends thereof. Specifically, referring to FIG. 1B in conjunction with FIG. 1A, note that the wicking arrangement 18 is located across one bend in the temperature profile of the tubes interior while wicking arrangement 20 is located across the other bend. More specifically, part of wicking arrangement 18 is subjected to the operating temperature within plasma tube 12 while part is subjected to a lower temperature, specifically the temperature below the vaporization temperature of the metal within the tube. This is also true for wicking arrangement 20. Under these conditions, each wicking arrangement serves to capture liquid metal resulting from the condensation of some of the metal vapor escaping from the active volume within tube 12 and causes the liquid metal so captured to be reintroduced into the active volume of the tube and reheated to its vapor state. This wicking process is well-known in the art and will not be described further, except as it relates to the present invention.
As stated above and shown in FIG. 1B, opposite ends of plasma tube 12 are cold, that is, below the vaporization temperature of the metal within the tube. This is because the electrode arrangements 14 and 16 are purposely maintained at cold temperatures, as it has been thought heretofore that the electrodes could not be operated at hot temperatures, specifically temperatures sufficiently high to vaporize the metal used in the plasma tube. As a result, in order to ensure that the wicking arrangements are in part hot and in part cold (which is necessary), heretofore they have had to be placed within the plasma tube in order to meet this condition and thereby function in the intended manner. This has a number of disadvantages. First, the active volume of the plasma tube itself, that is, the volume in which lasing takes place, is substantially shorter than the overall length of the tube. Second, each wick arrangement, because of its position within the plasma tube, takes up optical space that could otherwise be utilized in the production of the laser beam. Third, the wicks are placed directly in a relatively hostile environment whereby electrical discharge can take place in the wick itself. Fourth, the wicks and the liquid copper or other such metal can come in direct contact with the plasma tube, thereby reducing its operating lifetime by chemical degradation and fracturing during temperature cycling. These are some of the disadvantages associated with the prior art type of metal vapor laser illustrated in FIG. 1A.